One of the greatest dangers for first-responders when approaching a disaster site is their lack of incident-related information. This problem can be overcome by deploying and operating a range of high-performance sensors mounted on an unmanned aerial vehicle (UAV). For an initial survey and subsequently detailed reconnaissance of disaster areas where radiation sources represent a threat for rescue operations, the following specialized equipment can be used: the RIEGL VUX-1UAV laser scanner, a highly sensitive gamma radiation probe provided by CBRN Protection and the RiCOPTER-M UAV. An embedded processing and radio communication system integrated onboard the UAV enables real-time access to georeferenced 3D LiDAR pointclouds and gamma radiation levels. Precise localization of the gamma radiation sources and simulation of corresponding radiation activity patterns is achieved by automatic processing on the ground, taking the up-to-date topography into account. The results are displayed to the person in charge of response forces in an intuitive and user-friendly way on, e.g., a tablet computer in real-time and while the UAV is still in the air. Resolution and precision are continuously increased by a semi-autonomous flight path generation approach. This takes into account real-time radiation measurements in order to fly additional lines over automatically detected locations of specific interest. We present results of extended field tests with live radiation sources to demonstrate real-time data acquisition, processing, and refinement. The system shown represents a highly flexible and possibly life-saving asset for first-responders in time-critical scenarios.